1. Field of the Invention
The present invention relates to an image forming apparatus such as an ink jet printer and a medium exit device therefor.
2. Description of the Related Art
An image forming apparatus is provided with an image forming means and a medium conveyor device. For instance, a printer has a printing head to execute a printing operation and a conveyor device for conveying a medium (such as a paper sheet) in a predetermined direction past the printing head. The conveyor device comprises, for example, of a pickup roller, a feed roller and an exit roller, and a drive mechanism for driving such rollers is provided. The drive mechanism of the conveyor device generally comprises a motor and a gear train for transmitting the rotation of the motor to the conveyor rollers. The printer further comprises an exit tray (or a stacker) for receiving the printed medium. The printed media are stacked, on the exit tray, one on another.
In a printer, particularly in an ink jet printer, the printing operation is carried out by imparting a liquid ink to the medium. The ink imparted to the medium is gradually absorbed by the medium and dried. As the printing speeds of printers becomes faster, however, the time interval from an instant at which one medium is stacked on the exit tray to an instant at which a next medium is placed on the preceding medium, becomes shorter, with a result that a next medium is conveyed to the discharge tray before the ink of the medium at the top of the stacked media is sufficiently dried. If the next medium conveyed contacts the medium at the top of stacked media on the tray and rubs against the latter, the printed surface of the latter might become dirty and the quality of printing may be deteriorated if the ink on the medium on the tray is not sufficiently absorbed.
To solve such a problem, a printer having an exit tray and an auxiliary tray is proposed (for example, in Japanese Unexamined Patent Publication (Kokai) No. 11-5664). The exit tray and the auxiliary tray are located outside the casing of the printer, so that the auxiliary tray is disposed above the exit tray. The auxiliary tray comprises a plurality of tray elements adapted to be movable in the direction transverse to the sheet conveying direction. The conveyed paper sheet is temporarily placed on the auxiliary tray and then falls onto the exit tray when the auxiliary tray moves in the transverse direction, and is stacked on the exit tray. Next, the auxiliary tray returns to the original position onto which the subsequent paper sheet is conveyed and temporarily placed. These steps are repeated thereafter. By temporarily placing the paper sheet on the auxiliary tray, it is possible to provide a longer time period until this paper sheet is brought into contact with the sheet already stacked on the exit tray. Accordingly, the subsequent paper sheet can be placed on the preceding paper sheet stacked on the exit tray after the ink of the latter has sufficiently been dried. Thus, it is possible to prevent the printed surface from becoming dirty. Also, in another aspect, the auxiliary tray comprises a plurality of tray elements rotatable about an axis parallel to the sheet conveying direction, which operation is similar to that of the previous aspect.
In the prior art, however, the auxiliary tray comprises a plurality of tray elements movable transversely to the sheet conveying direction or rotatable about an axis parallel to the sheet conveying direction. Also, a drive mechanism of the auxiliary tray is disposed outside the casing of the printer. That is, in the prior art, the auxiliary tray and the drive mechanism therefor are formed separately from the body of the printer. Thereby, according to the prior art, an overall structure of the printer including the auxiliary tray becomes complicated to result in a high production cost, and a space occupied by the printer increases as a whole. Further, the auxiliary tray of the prior art is disposed outside the casing of the printer and cannot be accommodated within the casing of the printer.
The same problems reside in image forming apparatuses other than printers.
An object of the present invention is to provide an image forming apparatus and a medium exit device capable of preventing an image forming surface of a medium from becoming dirty even at a high sheet-conveying speed.
An image forming apparatus, according to the present invention, comprises an image forming unit, a conveyor device for conveying a medium in a conveying direction through the image forming unit, an exit tray receiving the medium having an image formed thereon, and an auxiliary tray disposed above the exit tray to be movable in the conveying direction.
According to this arrangement, the auxiliary tray is located outside the body of the image forming apparatus at a position above the main tray and movable in the conveying direction between a position above the main tray and another position at which it is retracted in the interior of the image forming apparatus. When the auxiliary tray is located at the position above the tray, the image is formed (for example, by the printing of letters or pictures) and the conveyed medium is temporarily placed on the auxiliary tray. When the auxiliary tray moves to the position retracted in the body of the image forming apparatus, the medium placed on the auxiliary tray falls onto the tray and is stacked thereon. Then, the auxiliary tray returns to the original position at which the subsequent medium is conveyed and temporarily placed on the auxiliary tray.
These steps are repeated thereafter. By temporarily placing the medium on the auxiliary tray, it is possible to have a longer time period until this medium is in contact with the preceding medium already stacked on the tray, so that this medium is placed on the latter after the ink of the medium previously stacked on the tray has sufficiently been dried. Accordingly, the contamination of the printed surface is avoidable.
In the present invention, the auxiliary tray is adapted to be movable in the direction parallel to the conveying direction of the medium, and therefore, may be formed of a single plate member. The auxiliary tray can be retracted into the interior of the body of the image forming apparatus. Thus, according to the present invention, it is possible to provide an image forming apparatus simple in structure and inexpensive in production cost as well as free from the contamination of an image forming surface of a medium even at a high conveying speed.
The image forming apparatus includes a printer, a copying apparatus, a facsimile machine or others. The image formation may be carried out by the ejection of ink.
The image formation includes not only the printing of picture but also that of letters.
Any media may be employed in the present invention, provided the image formation can be carried out thereon, and includes a paper sheet. In the printing, it is possible to form an image not only on the paper sheet but also on an OHP sheet or a fabric. The medium is not limited to the above-mentioned ones but includes those made of plastic or metal.
Preferably, a drive mechanism is provided for moving the auxiliary tray in the conveying direction. In this case, the drive mechanism of the auxiliary tray is operatively coupled to a drive mechanism of the conveyor device. Accordingly, the auxiliary tray moves in association with the movement of the medium to be conveyed, and the drive mechanism for the auxiliary tray can be extremely simplified in structure. Preferably, the drive mechanism of the auxiliary tray comprises a pinion driven by the drive mechanism of the conveyor device and a rack provided in the auxiliary tray to be engageable with the pinion.
Preferably, a frictional member is disposed in the drive mechanism for the auxiliary tray so that the auxiliary tray is driven by the drive mechanism of the conveyor device and also manually movable.
Further, according to the present invention, a medium exit device is provided, which comprises a conveyor device conveying a medium, an exit tray receiving the conveyed medium, and an auxiliary tray disposed above the exit tray and movable in the medium conveying direction. This medium exit device is simple in structure and inexpensive in production cost, and has an advantage in that the image forming surface is free from the contamination even at a high conveying speed.